Despite a battling performance from the third seed, Federer overcame him 7-6 (8-6) 5-7 6-1 in a memorable encounter at the O2.

And he was quick to heap praise on the talented world No. 3 in the immediate aftermath of the clash.

When asked what it felt like playing at Zverev’s age, he joked: ‘It was so long ago I hardly remember.

Zverev pushed him hard (Picture: Getty Images)

‘I don’t think I qualified until I was 21 in Shanghai. It was a dream for me to be part of it, where the best players take part and you can slog it out against them, knowing you’re only going to get better.

‘I’m excited for Alex’s future. He’s a wonderful guy and a great, great player.

Federer was made to sweat (Picture: Getty Images)

‘I’n happy and relieved that I can play freely against [Marin] Cilic, instead of it being a nail-biter. It’s been a tough group so to be through in two matches is great.

‘It was a good battle and I always enjoy myself at this beautiful arena. I have so much fun playing in London and I have been so successful here. Thank you for making it such a special night.’

Federer came out on top (Picture: Getty)

Fascinatingly, the pair could meet again in the final, should Zverev beat Jack Sock on Friday to book his spot in the last-four.

The duo will be split in their semi-finals, and the O2 crowd would no doubt love a repeat of that match to end the season.